Parachuting Frogs

August 11, 2011

What began as a joke resulted in a legitimate science experiment that involved more than 100 “parachuting” frogs. This summer three students are working with Biology Professor James “Jim” H. Benedix. Ashley M. Conard ’14, Stephen G. Hesterberg ’13 and Luke B. Miller ’14 admit they were pleased and surprised when their brainstorming session that included some kidding around led them to a very interesting and rewarding research experience.

They designed an experiment to study the falling behavior of frogs – a behavior that is referred to as parachuting. “As the students tried to come up with project ideas, Luke shared what he learned in a physics class from an earlier cat study, which you couldn’t possibly do now,” Benedix says. “The project involved dropping cats from different heights to see them get into their falling behavior and try to land effectively.

“Luke asked jokingly, ‘Could we drop frogs off the roof?’ My answer was, ‘No,’ but I said that there are times when weather conditions are right, and frogs are heading to the pond in such a hurry, that they literally are jumping out of trees.

“All this time, the idea had been a big joke telling stories about frogs,” Benedix explains. “Finally, I realized that this is a legitimate behavior, and it’s something that we should understand because clearly, not all frogs should be able to do it. There should be adaptations for allowing the frog to jump out of trees and not die when they land on the ground.

“We did some more background research and discovered that the behavior is called parachuting, when some animals drop directly down and try to slow their decent. In cases where they move laterally, it is referred to as gliding,” Benedix explains. “We decided to compare frogs that live in trees and ones that don’t. The hypothesis being that the species that lives in trees is going to be better at falling and will do something that allows them to drop at a slower speed.

“We built a 12-foot high wall, painted it like a ruler and set up two video cameras,” Benedix says. “From the front, we could videotape the frogs falling in front of the ruler, and a smaller camera took MP3s from the top to show that the frogs were actually doing the correct behavior. We put a pool at the bottom so that they had a soft place to land – if they were really bad at falling.

“The students figured out a way that they could throw the frogs into the air and actually videotape them. The next step was to figure out a way to calculate the differences in acceleration,” Benedix says. “It took a while to create a formula to measure from the videotaping because it was limited. You could only get one frame every 30th of a second. So, you couldn’t precisely time them using the video, but you could measure how far they moved over a known amount of time.”

Benedix explains that if you think of gravity as being like a gas pedal, the frogs that are good parachuters have their foot off the gas more than the ones who are bad parachuters and have their foot to the floor.

The students decided to add toads to the experiment because the toads have always been on the ground. “We figured the frogs were going to fall really fast, and we wanted to have a comparison. We had frogs that were fully awake and warm, and also chilled some of them so that their reactions would be slowed and they wouldn’t be very good at performing the behavior. We wanted to show not only that there is a difference between species, but also find within a species, do they fall less well when they’re groggy?

“The students started the experiment and found that the frogs that were chilled were still throwing their arms out,” Benedix says. “So we needed an extra comparison. We asked for permission from the Animal Care Committee to take a small sample of two of the three species and anesthetize them. They fell like rocks.

“We just finished analyzing the data, and in the end, it didn’t matter whether they were cold and sort of throwing out their arms in a slower, awkward way or if they were anesthetized, they all dropped at about the same speed. Basically, if you were a fully awake tree frog, you were pretty good at slowing yourself down.

“The cricket frogs, which are in the tree frog family but live on the ground, were also good at it but not quite as good as the tree-dwelling frogs. There actually was a difference between them. After that, it didn’t matter if you were a toad, cold, anesthetized; you just dropped like a rock. It was clear that the tree frogs do use the behavior, and if they are arboreal frogs, they have perfected it. The cricket frogs can do it but just don’t do it as well.

“The importance of the study is that we were able to document the first step in the evolution of what could eventually become gliding behavior,” Benedix says. “It appears that in the species we studied, the behavior did evolve. The tree-dwelling frogs have a very precise behavior that slows them down. If they were in a situation where it was crucial because they were jumping out of trees much more than I think they probably are now, then you’d expect those morphological traits to evolve, too. However, it’s just the behavior that they have at this point.”

Benedix says, “This was the best kind of project because it was totally unanticipated and turned into something really interesting, but started off as something just silly.”

Hesterberg agrees. “I never thought we’d actually be doing this project and turning it into real science. It’s given me the chance to experience ecology research and understand what the research process is really like.”

“It’s a great feeling to know that one of our first research projects – which was completely a joke in the beginning – turned into something that is of value to the science community,” Conard says. “The experiment didn’t look as complicated as it was, but when you start with nothing, and have to completely imagine how you want it to look, it was challenging. We got the results we expected, which is a very rewarding feeling after so many hours of work.”

Conard, Hesterberg and Miller are Science Research Fellows (SRF), which is an honors program for outstanding students interested in studying science and having significant hands-on research experiences as undergraduates. The program prepares students to be top candidates for post-graduate study and for a wide variety of careers in science. To learn more about the program, click here to visit the SRF website.